The present invention relates to a method and an apparatus for safety control of the drying cycle in hydrocarbon-solvent dry-cleaning machines.
Dry-cleaning machines are known which use as solvent, instead of perchloroethylene, a group of petroleum-derived solvents formulated appropriately for dry-cleaning, particularly paraffin hydrocarbons such solvents are becoming widely used due to their low environmental impact.
Solvents of the hydrocarbon group suffer drawbacks due to danger of explosion under certain conditions: above a certain temperature level, known as flash point, if the concentration of the solvent in the air is between two values, known as lower and upper explosion limits, which are specific for that particular type of solvent, if a spark occurs the mixture of air and solvent can explode.
Situations entailing the danger of explosion occur in practice during the drying cycle, during which hot air is introduced in the washing drum that contains the moist laundry in order to extract the solvent from the laundry: the hot air, saturated with solvent, is passed through a cooling radiator, where the solvent condenses and is separated from the mixture; then the air is heated again in a heating radiator and returned to the drum.
It is known in the art to provide a portion of drying circuit in which the outlet of the drum is connected to a cooling radiator of a refrigeration unit, to a heating battery and then to the inlet of the drum. In order to provide safety control over the possibility of explosion of the dry-cleaning machine, it is known to install, at the outlet of the drum, a device for measuring the concentration of solvent; in certain machines, the concentration measurement device operates the shutdown of the heater when particular values of concentration, linked to the measurement of the temperature of the air-solvent mixture at the outlet of the drum, are exceeded.
However, these dry-cleaning machines suffer the drawback that at the beginning of the drying cycle, when the presence of the solvent and the danger of explosion are the highest and when it would be necessary to cool rapidly and more efficiently the mixture of air and hydrocarbons, which is too rich in hydrocarbons, the effectiveness of the system for cooling and therefore separating the solvent from the air is inadequate; in order to avoid the danger of explosion, one is forced to mainly act only on the interruption of the heating of air before returning it to the washing drum, and this leads to an undue increase in drying times.
Moreover, concentration detection devices for known dry-cleaning machines are rather expensive and delicate and have relatively long response times.
The aim of the present invention is to obviate the above mentioned drawbacks of the prior art and meet the mentioned requirements, by providing a method for safety control of the drying cycle in hydrocarbon-solvent dry-cleaning machines which avoids reaching dangerous concentrations of hydrocarbons, speeds up the drying cycle and provides a corresponding apparatus which is extremely reliable, not delicate and having very rapid response times.
Within this aim, an object of the present invention is to provide a method and an apparatus which is simple, relatively easy to provide in practice, safe in use and effective in operation.
This aim and these and other objects which will become better apparent hereinafter are achieved by the present method for safety control of the drying cycle in hydrocarbon-solvent dry-cleaning machines, characterized in that in the first step of the drying cycle, when the temperature of the mixture of hot air and solvent at the outlet of the drying drum reaches values which are higher than a preset safety value, the air, before being returned to the drum, is passed through an additional separator-heat exchanger having a high thermal capacity.
The apparatus for carrying out the method of the invention is characterized in that it comprises an additional heat exchanger having a high thermal capacity, which is connected to the drying circuit of the machine by way of at least a valve which is driven by a detector for detecting the temperature of the air-solvent mixture that leaves the drum, at least part of the drying air being passed, above a preset temperature, through the additional exchanger instead of through the drum.